1. Field
The present disclosure relates to a tire assembly comprising a mounting rim and a tire with radial carcass reinforcement and more particularly to a tire of the light heavy-weight (light truck) type intended to be fitted to a vehicle such as a van. It relates more specifically to a new bead structure for such tires.
2. Description of Related Art
In general, a tire of the kind considered comprises a carcass reinforcement formed of at least one ply of metal cords or textile cords, this carcass reinforcement being anchored in each bead to at least one bead wire, forming a turned-back portion. The carcass reinforcement is radially surmounted by a crown reinforcement, made up of at least two plies of metal cords which are crossed from one ply to the next, making angles of between 10° and 45° with the circumferential direction. The turned-back portion of carcass reinforcement comprises, when viewed in a radial plane of section (which means a plane containing the axis of rotation of the tire) one end situated in an appropriate distance away from the axis of rotation of the tire so as to ensure good mechanical anchorage of the bead when the tire is in use. Between the carcass reinforcement and the turned-back portion there are one or more profiled elements based on rubber compounds.
This tire is intended to be mounted on a mounting rim comprising a part (known as the rim seat) intended to accept the beads of a tire and, axially on the outside of each seat, a flange intended to limit the axial movement of the beads of the tire at the time of inflation. It is well known that one same light truck or van tire can be mounted on a number of rims having different flange geometries. What is meant here by different geometries is that these rims differ in terms of different flange heights and different rim hook curvatures. Depending on the height and shape of the rims, it will be readily appreciated that stress levels may be particularly penalizing to the endurance of the beads and therefore that of the tire. The most penalizing situation is obtained with low rim heights and rim hooks with small radii of curvature.
Solutions have been put forward for improving the endurance of the beads of such tires. In particular, U.S. Pat. No. 5,433,257 describes a bead structure in which a first profiled element of triangular section bears against the bead wire of circular section and extends, tapering radially outwards, as far as a point situated substantially at the same height as the end of the turned-back portion of carcass reinforcement. This first profiled element is pressed firmly against the carcass reinforcement. Furthermore, a second profiled element extends the first out to a point radially on the outside of the end of the turned-back portion; this second profiled element provides the connection by contact between the first profiled element and the turned-back portion of carcass reinforcement. The first profiled element is made of a material having an elastic modulus at 100% extension that is equal to 6 MPa while the second profiled element is made of a material having an elastic modulus at 100% extension that is equal to at least 1.5 MPa and at most equal to 3.5 MPa.
In the structure according to the prior art and in a radial plane of section, which means a plane containing the axis of rotation, the distance to the axis of rotation of the end point of the turned-back portion is greater than the distance of the point of the mounting rim on which the tire is intended to be mounted. Finally, an additional reinforcement comprising a plurality of reinforcing elements making an angle different from the angle of the reinforcement elements of the carcass reinforcement is provided, in order partially to envelop the turned-back portion and the carcass reinforcement in the bead. Rubber compounds are also provided to decouple the turned-back portion from the additional reinforcement. Further, a profiled element is provided axially on the outside of the additional reinforcement in order to rest against the rim flange.
This structure, despite having good endurance performance, confers additional weight upon the tire and it is known that additional weight is something particularly closely monitored in the development of new light trucks and vans.
The sought-after objective is a tire bead structure for light trucks and vans which is lighter in weight without that leading to a loss in performance, particularly in mechanical integrity as the beads heat up as a result of repetitive braking. Research conducted by the applicants has revealed that the bead structures recalled above can be markedly improved through a careful choice of the profiled elements and of the rubber-based materials of which the tire beads are made.